Vehicles are tested extensively for many different performance characteristics such as fuel economy, aerodynamic drag, noise, vibration and harshness, and for many other reasons. Tests developed over the years for internal combustion powered vehicles resulted in establishing standards that are now being applied to hybrid vehicles, partial hybrid vehicles and electric vehicles. Normal vehicle sign-off procedures require verification of drive times, speeds, and loads that may be outside the normal operating capabilities of most electric vehicles. Test engineers may also need to disengage from the tow vehicle to allow for “free maneuvers” or unique drive evaluations. There is also a need to allow drivers of towed and towing test vehicles to release and steer clear of each other in case of emergency.
Land vehicles are tested for aerodynamic drag and mechanical drag in a test that is known as a “Certification Coast Down Test” that is specified in SAE J2263 DEC2008. The Certification Coast Down Test requires vehicles to be towed at unusually high speeds (over 115 km/h) for extended periods of time. In the Coast Down Test, a vehicle is normally driven to reach a speed of 115 km/h at which point internal combustion powered vehicles are shifted to neutral and allowed to coast until a speed of 15 km/h is reached. The time required to coast until reaching the lower speed is measured and analyzed.
Drivetrains of hybrid vehicles and electric vehicles are difficult, or impossible, to disconnect while the vehicles are moving. Hybrid vehicles and electric vehicles cannot use their own drivetrain to accelerate the vehicle to the desired speed to start the test because the electrical portion of the drivetrain cannot be completely disconnected while the vehicle is moving. One way to accelerate hybrid and electric test vehicles is to push the vehicles from the rear but this approach may damage the test vehicle and it is difficult to control. Towing such vehicles to reach the desired speed is unacceptable because the towing vehicle may interfere with the test results by disturbing the air flow around the test vehicle. The towing cable, if not released from the towed vehicle, may interfere with the test results.
Glider aircraft are normally towed to reach a desired altitude and are released by a cable release mechanism. This approach to releasing a towed glider is simple and effective but requires a cable guide system and can only be operated by the pilot of the towed or towing aircraft.
This disclosure addresses one or more of the above problems and other problems as summarized below.